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Trail and greenway design under road bridges

Trails along streams are often crossed over by highway and railroad bridges. These crossing points are often located where the stream narrows. The first challenge is to design a trail that goes under the bridge with enough headroom. The second challenge is to provide a bench for the trail on a narrow, steeply-sloping riverbank. Retaining structures and vertical concrete walls are typical solutions. Armoring the trail edge with rock is a common solution where the slope down to the water is moderate. Large culverts may also provide the opportunity to cross under major roadways with minimal expense. The normal flow is channelled through one or more culverts and the trail is built on a raised concrete bed through an outer box. In the case of smaller streams with lower bridges, the trail may have to be built below high water level. In recent years designers have been building flood walls between the trail and the stream, so that the trail surface is well below the typical flowing water level. See photos 11 and 12, and 17-19 for examples of this solution.

See articles and resources on trail bridges and structures and more on greenways and riverways

Photos by Stuart Macdonald; click on any photo to see it full size:

Schuykill River Trail crosses under both road and rail bridges, Philadelphia, PA; photo by Stuart Macdonald, October 6, 2008

Schuykill River Trail requires a significant grade to go under bridges, Philadelphia, PA; photo by Stuart Macdonald, October 6, 2008

Schuykill River Trail, Philadelphia, PA; photo by Stuart Macdonald, October 6, 2008

New road bridge built over a minor drainage accomodates trail in Stapleton "new urbanism" development, Denver, CO; photo by Stuart Macdonald, April 13, 2008

Rip-rap rock keeps flood water from undermining trail; Stapleton community, Denver, CO; photo by Stuart Macdonald, April 13, 2008

Vertical walls along Cedar River provide room for trail without grade changes, Renton, WA; photo by Stuart Macdonald, September 27, 2006

Cedar River Trail has brick surface with concrete side wall, Renton, WA; photo by Stuart Macdonald, September 27, 2006

C and O Canal trail in Georgetown, Washington, DC; photo by Stuart Macdonald, June 16, 2007

Waller Creek Trail is built on concrete pad in flood channel, Austin, Texas; photo by Stuart Macdonald, July 15, 2007

High bridge over Town Lake in Austin provides plenty of room for trail; photo by Stuart Macdonald, October 28, 2006

Low bridge over Truckee River requires trail to drop below river level, Reno, Nevada; photo by Stuart Macdonald, March 9, 2008

Detail of wall between Truckee River and trail, Reno, Nevada; photo by Stuart Macdonald, March 9, 2008

Triple culvert provides opportunity to route trail under highway; Clear Creek Trail, Jefferson County, CO; photo by Stuart Macdonald, August 1, 2009

Trail tread is concrete built up above normal water level; Clear Creek Trail, Jefferson County, CO; photo by Stuart Macdonald, August 1, 2009

Concrete trail provides protection against seasonal flooding; Clear Creek Trail, Jefferson County, CO; photo by Stuart Macdonald, August 1, 2009

Triple culvert provides opportunity to route trail under highway; Clear Creek Trail in west Denver suburbs; photo by Stuart Macdonald, August 1, 2009

Approaching crossing under road bridge, Clear Creek Trail, Wheat Ridge, Colorado, TX; photo by Stuart Macdonald, August 1, 2009

Concrete wall enables trail surface to be below water level, Clear Creek Trail, Wheat Ridge, Colorado, TX; photo by Stuart Macdonald, August 1, 2009

Note height and thickness of walls along Clear Creek Trail, Wheat Ridge, Colorado, TX; photo by Stuart Macdonald, August 1, 2009

Trail is built on concrete wall under major bridge over Schuykill River, Philadelphia, PA; photo by Stuart Macdonald, October 6, 2008